From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 6E1623857433; Thu, 26 May 2022 11:22:31 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6E1623857433
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/105739] New: [9/10 Regression] Miscompilation
 of Linux kernel update.c
Date: Thu, 26 May 2022 11:22:31 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.3.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
 cf_gcctarget
Message-ID: <bug-105739-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Thu, 26 May 2022 11:22:31 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105739

            Bug ID: 105739
           Summary: [9/10 Regression] Miscompilation of Linux kernel
                    update.c
           Product: gcc
           Version: 10.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---
            Target: x86_64-linux

The attached testcase with -fno-strict-aliasing -fno-common -fshort-wchar
-fno-PIE -std=3Dgnu11 -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
-fcf-protection=3Dnone   -m64 -falign-jumps=3D1 -falign-loops=3D1 -mno-80387
-mno-fp-ret-in-387 -mpreferred-stack-boundary=3D3 -mskip-rax-setup -mtune=
=3Dgeneric
-mno-red-zone -mcmodel=3Dkernel -fno-asynchronous-unwind-tables
-mindirect-branch=3Dthunk-extern -mindirect-branch-register -fno-jump-tables
-fno-delete-null-pointer-checks -O2 --param=3Dallow-store-data-races=3D0
-fstack-protector-strong -fomit-frame-pointer -fno-stack-clash-protection
-fno-strict-overflow -fno-stack-check -fconserve-stack
options has a call to _printk replaced by __builtin_unreachable () and it i=
sn't
obviously clear why.

One spot is in the rcu_tasks_trace_pertask function where in assembly one c=
an
see:
        .type   rcu_tasks_trace_pertask.cold, @function
rcu_tasks_trace_pertask.cold:
.L1662:
        movl    20(%rdi), %eax
        .text
        .size   rcu_tasks_trace_pertask, .-rcu_tasks_trace_pertask

The problem went away with r11-5188-g32934a4f45a7214 but it is unclear if
that was an actual fix or just made it latent, I don't see a compound liter=
al
on that line.=